Exemplary embodiments of the present invention relate to an exhaust gas aftertreatment device for a combustion engine, in particular of a motor vehicle.
German patent document DE 197 31 865 A1 discloses an exhaust gas aftertreatment devices for a combustion engine, in particular of a motor vehicle. The exhaust gas aftertreatment device referred to therein as exhaust gas purification facility comprises a guide element in the form of an exhaust gas tube, through which exhaust gas can flow, as well as a dosage device. Using the dosage device a reduction agent for aftertreatment of exhaust gas can be introduced into the guide element at least at one feed point. This means that in the course of the exhaust gas aftertreatment the reduction agent is supplied to the exhaust gas flowing through the guide element.
The exhaust gas aftertreatment device also comprises at least one interference element, which is arranged upstream of the feed point within the guide element. The exhaust gas flows towards the interference element, which—for supporting an intermixing of the exhaust gas with the reduction agent—causes turbulences in the flow of the exhaust gas. The interference element thus is employed as mixing device so that the exhaust gas, due to the turbulences caused in its flow, intermixes with the reduction agent.
The reduction agent commonly is urea, which is present in an aqueous urea solution. The reduction agent usually is stored in a tank of the motor vehicle and carried along in the tank.
The exhaust gas and the reduction agent contained in the exhaust gas commonly flow to an SCR catalytic converter (SCR—selective catalytic reduction), by means of which a reaction of the exhaust gas, and in particular of the nitrogen oxides (NOx), with the ammoniac (NH3) contained in the reduction agent is caused. In the course of this reaction the ammoniac reacts with the nitrogen oxides to produce water and nitrogen. The reduction agent thus is used for the so-called denitriding of the exhaust gas.
A good intermixing of the reduction agent with the exhaust gas has an advantageous effect upon the described reaction. This means that for denitriding the exhaust gas only a very small amount of reduction agent needs to be supplied to the exhaust gas, if a good intermixing of the exhaust gas with the reduction agent is realized. If only a very poor intermixing is realized, a correspondingly larger amount of reduction agent needs to be supplied to the exhaust gas. This leads to a correspondingly fast exhaustion of the tank. In order to nevertheless realize particularly long periods between two filling operations of the tank, the tank can be equipped with a correspondingly large intake capacity. This, however, requires a very large quantity of reduction agent and thus requires a large weight increase of the motor vehicle.
Exemplary embodiments of the present invention are directed to an exhaust gas aftertreatment device providing a particularly good intermixing of the gas with the reduction agent.
In order to further develop an exhaust gas aftertreatment device for a combustion engine, in particular of a motor vehicle, in such a way that a particularly good intermixing of the exhaust gas with the reduction agent is realizable, it is envisaged according to the present invention that the guide element comprises at least one first guide portion, through which the exhaust gas can flow in a first flow direction, and at least one second guide portion, through which the exhaust gas can flow in a second flow direction that is contrary to the first flow direction. In other words, during operation of the combustion engine the exhaust gas flows through the first guide portion in the first flow direction, whilst the exhaust gas flows through the second guide portion in the second flow direction that is contrary to the first flow direction. The second flow direction thus relative to the first flow direction is a counter direction.
The guide element further comprises a third guide portion, which redirects the exhaust gas from the first flow direction into the second flow direction and via which the first guide portion and the second guide portion are fluidically connected with each other. This means that the exhaust gas initially flowing through the first guide portion flows from the first guide portion into the third guide portion and is redirected by means of the third guide portion. Finally, the exhaust gas flows from the third guide portion into the second guide portion.
The feed point and the interference element in this setup are arranged within the third guide portion, wherein the interference element has at least one flow through opening for the exhaust gas. The interference element thus is a perforated baffle, towards and through which the exhaust gas can flow and which causes turbulences in the flow of the exhaust gas.
By virtue of this design of the exhaust gas aftertreatment device particularly advantageous turbulences of the flow of the exhaust gas are caused so that the exhaust gas intermixes very well with the reduction agent. Firstly, the turbulence introduced by the interference element will enhance intermixing between exhaust gas and reduction agent. More importantly, the interference element changes the flow field in the third guide portion, which allow intermixing take place further upstream (in the third guide portion) than the case without the interference element. In addition, the early section of the second guide portion is also better utilized for intermixing since stronger swirl is formed there due to the changed flow field by the interference element in the third guide portion. All these factors contribute significantly to achieving even reduction agent distribution at SCR catalyst. As a consequence, when denitriding the exhaust gas even with a very small amount of reduction agent, particularly high conversion rates can be realized. Accordingly, a tank for storing and transporting the reduction agent can have a particular small intake capacity. Nevertheless, large time intervals between the two maintenance instants, at which the tank is filled with reduction agent, are realizable.
Moreover, the exhaust gas aftertreatment device due to guiding of the exhaust gas in the two contrary flow directions requires only very little construction space so that packaging problems can be solved and/or avoided. Moreover, the interference element can be configured to have a particularly low complexity, i.e. a particularly simple design with regard to its structure, so that the exhaust gas aftertreatment device involves only very small costs.
For realizing a particularly advantageous intermixing in one embodiment of the invention the interference element has a plurality of flow through openings for the exhaust gas.
It has turned out to be further particularly advantageous if the interference element, at least in one partial area, is designed as surface element extending at least essentially perpendicularly to the flow direction of the exhaust gas in the third guide portion. The interference element thus, at least in one partial area, has a particularly simple structure and can be produced at low cost.
If the flow through openings are arranged in the partial area, turbulences of the flow of the exhaust gas that are very advantageous for the intermixing can be caused. Moreover, the flow through openings can be provided in a simple and cost-efficient way in the partial area.
In a further advantageous design of the invention the interference element has a flange extending at least essentially at an angle or perpendicularly to the partial area, via which flange the interference element is connected to the third guide portion. This allows a simple mounting of the interference element on the third guide portion. The interference element may be screwed and/or glued and/or welded together with the third guide portion or connected in any other way with it.
In a further embodiment of the invention the third guide portion has a flow cross-section through which the exhaust gas can flow. The flow cross-section comprises a first partial area and a second partial area. The interference element in this connection is arranged in the first partial area and the exhaust gas can flow around it via the second partial area. In other words, the exhaust gas flowing through the third guide portion flows towards the interference element in the first partial area, with the interference element not being arranged in the second partial area. Accordingly, in the second partial area the exhaust gas does not flow towards the interference element. The second partial area thus is free of the interference element.
In this connection the second partial area, in which the interference element is not arranged, can be larger than the first partial area. Accordingly, an increase of the exhaust gas counter pressure caused by the interference element can be avoided or at least be kept to a minimum. This advantageously affects charge changes of the combustion engine, which is for instance configured as internal combustion reciprocating piston engine, and leads to an efficient operation at low fuel consumption. At the same time, by means of the interference element a very good intermixing of the exhaust gas with the reduction agent is realizable so that local accumulations of the reduction agent in the exhaust gas can be avoided.
In a further advantageous embodiment of the invention the interference element has at least one side that, in one area of a wall of the third guide portion, contacts the wall and is adapted in its outer contour to the area of the wall. Thereby, a defined guiding of the exhaust gas can be realized, since it cannot flow through between the partial area of the wall and the interference element.
Further advantages, features, and details of the invention derive from the following description of preferred embodiments as well as from the drawings. The features and feature combinations previously mentioned in the description and the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be used not only in the respective indicated combination, but also in any other combination or taken alone, without leaving the scope of the present invention.
In the figures same elements or elements having same functions are equipped with same reference signs.